View Full Version : 21ax gassy or bad 3a3?


SwizzyMan
12-31-2015, 08:10 PM
Just got my CTC-5 home from tvdude1. I had an image on the 21axp22 for about a minute before I turned the set off. Came back about 5 or 10 minutes later and noticed I couldnt get a picture anymore but I had HV. I looked at the gap between the G2 element of the electron gun and the other element and saw a faint blue glow. But then I noticed the 3a3 HV rectifier had a ring of brighter blue around the whole envolope. This all starts when the HV starts up. The 3a3 tests OK on my 600A and the 21ax tests perfect on all guns. The cutoff test on all guns performs nicely and is not jumpy and I can get it to hold in the cutoff set line. Could this be a HV issue or something wrong with the 3a3 or could my 21ax be gassy all of the sudden? :tears:

Eric H
12-31-2015, 08:21 PM
More likely the 3A3 went bad, it shouldn't glow blue. It might check okay because your tester isn't putting 20kv on it.

A small amount of blue glow between the elements of a tube can be normal, if the whole neck glowed purple than I'd worry.

SwizzyMan
12-31-2015, 08:27 PM
swapped the 3a3. The new 3a3 glows still and the blue glow between G2 is still there. Anyone else know what might be happening?

DaveWM
12-31-2015, 09:55 PM
if it has HV and the CRT test good, then it HAS to be a bias issue or focus voltage. check both.
oh and a pic would help, blue glow sounds harmless, purple is bad, but better to let us see pic is worth a thousand words.

Username1
12-31-2015, 10:26 PM
In your opinion do the heaters look like they are normally lit on the picture tube ?
Also, you should take a HV reading and see if it's normal..... +18K for a 5....
Did you do an actual HV reading with a meter.....?

.

miniman82
01-01-2016, 12:18 AM
Check/replace your focus rectifier, no focus voltage will make a CRT not show a picture all else being the same. If it's not that, at least make sure focus voltage is making it to the CRT socket. Could also be the last video tube in the chain, if it died a sudden death any number of maladies could be haunting it.

SwizzyMan
01-01-2016, 12:40 AM
Will do later this morning, accidentally pulled a socket pin out of the socket assembly while removing the CRT socket so will have to fix that first. I highly doubt the CRT is gassy if it can survive over 1300 miles of bumpy highways it can survive sitting in the 76 degree house I live in. Anyone have a general idea of how durable the 21axp22 is in terms of taking off the socket and putting it back on plus the bumpy ride home? Also happy New Year to all you folks here!

tvdude1
01-01-2016, 09:05 AM
Have you recapped the set and also 2 of the main filters were leaking really bad. It was all original.

Username1
01-01-2016, 09:15 AM
I think that tube only has a 1200 mile bumpy road rating.....

:)

.

jr_tech
01-01-2016, 02:19 PM
Did you check the 12BY7 second video amp?

jr

Electronic M
01-01-2016, 02:30 PM
Sounds like it needs a recap....When an un-recaped set of that age starts loosing function it's time to change caps. You should verify all the B+ voltages.

In addition to the focus voltage G2 is important. If G2 is low from a bad B+ boost supply the screen won't light.

ohohyodafarted
01-01-2016, 03:07 PM
Will do later this morning, accidentally pulled a socket pin out of the socket assembly while removing the CRT socket so will have to fix that first. I highly doubt the CRT is gassy if it can survive over 1300 miles of bumpy highways it can survive sitting in the 76 degree house I live in. Anyone have a general idea of how durable the 21axp22 is in terms of taking off the socket and putting it back on plus the bumpy ride home? Also happy New Year to all you folks here!

OK lets use correct terminology. The end of the picture tube has a bakelite "base" with pins. The wires from the chassis has a "socket" that has "terminals" inside of it.

Are you saying you pulled a "PIN" out of the Bakelite "base" on the 21AX or did you pull a "terminal" out of the "socket" that hase wires connected to the chassis.

First, I do not think your 21AX went bad, but that is always a possibility. If your tube is gassy you would probably get the dreaded purple neck glow when you power the chassis up. 10 years ago I purchased a CTC5 Wingate from California. The seller told me it was operational a year prior to when I purchased it. It was shipped to me in Wisconsin and when it arrived the crt was gassy. I am not sure if it was the transportation or temperature changes that made it go gassy but it sprang a leak at the weld line. The usual place that a 21AX leaks is on the heli-arc weld where the front of the tube is joined to the rear funnel. It is very rare for a leak to form where the glass components are fused to the metal parts of the tube. It is even more rare for a leak to happen where the lead wires come through the stem under the Bakelite base.

Normally if a crt is gassy, the filaments will be very dim with 6.3 volts applied. And if you increase the voltage while under test on a tube tester the filaments will usually burn out.

Follow up on suggestions the other posters gave to see if you have focus and ultor voltages. Then see if you have video signals and correct bias voltages at the pins on the crt.

old_coot88
01-01-2016, 03:46 PM
...Normally if a crt is gassy, the filaments will be very dim with 6.3 volts applied. And if you increase the voltage while under test on a tube tester the filaments will usually burn out.
If the tube has gone completely to air, another symptom is quickly apparent:
the cathode end of the neck gets really really hot, immediately. Like too hot to touch. And the heaters may not light visibly, because of being
immersed in a heat-conducting fluid (air). And the heaters pull 'waay too much current since they can't come up to full temperature.
If you put a tester on it, the transformer in the tester may be unable to supply that much current.

SwizzyMan
01-01-2016, 05:34 PM
Sorry about the confusion. I pulled a terminal out of the socket that plugs in to the CRT base. Will do a chassis and replace the filters and work from there. But it is confusing that 10 minutes after I last had a raster I wasn't able to get one again. Now when I try and power up the set without the CRT plugged into the socket once the hv comes up about 2 seconds later I hear a pop from the cage I immediately turned the set off. I think this set just needs a full recap with some resistor replacement. I wanted to turn it on just to get a baseline.

tvdude1
01-01-2016, 05:37 PM
I sold this set it had very good raster and with a vcr had all 3 good colors but lousy sync. It was fine the night before he picked it up. He is trying to run this old timer with bad filters and waxed caps. I had disconnected a can and jumped it to just make it light up.

SwizzyMan
01-01-2016, 07:02 PM
The longest I ran it was for about 4-5 mins this was when I could get a nice bright raster. I noticed an 80uf sprague atom was tacked on to the existing 80uf section in the filter capacitor. That isn't good since the original capacitor could mess with the tacked on 80uf. I also noticed that another filter cap was leaking a bit of PCB infused gunk out of one section. This set needs a nice full recap and that is what I plan on doing before I power up the set again. Will create a separate thread about this set soon. At least I know my 21ax is good!

bgadow
01-01-2016, 10:50 PM
Probably not related, but when I first brought home my ctc-5 it worked okay. The next day I couldn't get a raster. It took me a long (really long) time to figure out what had happened. There is a shield attached to the underside of the chassis and when I took it off there were "crispy critters". A cap/resistor that had shorted. Again, probably not your issue, but don't forget to look under that shield.

holmesuser01
01-05-2016, 10:56 AM
I'm running, and working on, a CTC-7 with an original CYP22 in it.

When it's warming up, I get a momentary glow of blue in the neck of the CRT just as high voltage comes up. It's always gone before the screen lights.

The 3A3, which is an original with the set glows blue for just a moment around the gap between the plate and cathode.

This set is almost totally original... a total of 2 tubes replaced by me.

Perfectly normal for me over the years.

bgadow
01-05-2016, 10:49 PM
I had a CTC-31 with an intermittent connection in the video output section. When it would lose the video the neck of the crt would glow bright purple. The crt was fine.

SwizzyMan
01-06-2016, 07:57 PM
Almost all 4 filter caps were completely fossilized. I restuffed the cans and now I have no HV with the chassis on the bench out of the cabinet. Dont see the 3a3 or the 1V2 glowing. everything else seems to be OK. No magic smoke just no HV at all I cant even hear any sort of high voltage whine from the flyback. I have been reading over the schematics and I cant seem to figure this out.

Electronic M
01-06-2016, 08:16 PM
Almost all 4 filter caps were completely fossilized. I restuffed the cans and now I have no HV with the chassis on the bench out of the cabinet. Dont see the 3a3 or the 1V2 glowing. everything else seems to be OK. No magic smoke just no HV at all I cant even hear any sort of high voltage whine from the flyback. I have been reading over the schematics and I cant seem to figure this out.

Probably won't do much HV wise without the yoke hooked up (The sweep circuits go out of tune without the yoke, and RCA often put jumpers that complete the HV B+ wiring in the yoke plug to prevent sweep circuits from running without it connected). Reconnect the yoke, then if it still ain't producing HV make sure the bias voltages on the Horizontal output tube are correct.

miniman82
01-06-2016, 08:32 PM
Tom's right, RCA's and probably others won't work with the yoke disconnected. I made an octal jumper plug to replace the yoke when I run sets on the bench, just for that reason. You can make one yourself, just break any useless octal tube and harvest the socket. Remove the remnants of the old lead wires, and jumper pins 3 and 7 together. Works on all RCA chassis CTC-2 through CTC-5. CTC-7 and later had spade connectors for the yoke, so the horizontal sections will run without jumpering anything.

SwizzyMan
01-06-2016, 08:41 PM
That did it. Thanks Nick! 6BK4 now has its spooky green glow again!

SwizzyMan
01-08-2016, 05:53 PM
Changed the damper and H-out and now when hv comes up I get a bunch of weird sounds from the flyback lower pitched squeals. I put the original tubes back in and I still have this issue. Is the flyback going bad or is there arcing somewhere possibly.

Username1
01-08-2016, 06:01 PM
The yoke which is a coil, makes up a tank circuit with a capacitor that makes up part
of the B+ Boost, and load on part of the flyback. All of these are tuned. Jumping
a short across the coil on the yoke surly has an effect on the rest of the sweep
circuits. Even if some have jumped something and not had anything go wrong, I would
say it's not a good idea..... Especially if you are trying to troubleshoot something in
that area of the set....

For your problem, you need to check to be sure items in the area are working
as best you can... Voltages at the different points on the picture tube. (Bias -
Gx pins, Focus, HV, Horiz output tube Cathode current in range, sweep circuits
working, etc. )

.

SwizzyMan
01-08-2016, 06:06 PM
But I find it odd that it would just now start this...

old_tv_nut
01-08-2016, 06:58 PM
Squeals could be arcing, but also could be the H oscillator not running properly. An oscilloscope is really useful for checking this out.

SwizzyMan
01-08-2016, 09:20 PM
Turns out the the new 6CG7 horiz osc had a short in it and so did the new damper. Replaced those with the originals and got my HV back. Is it normal for the HV to only measure 4-6 kilovolts without the crt or yoke plugged in? I am running the chassis on the bench.

old_tv_nut
01-10-2016, 10:59 AM
Is it normal for the HV to only measure 4-6 kilovolts without the crt or yoke plugged in? I am running the chassis on the bench.
I have no idea, but I'm not surprised. Running without the yoke doesn't seem wise, as the system is tuned to resonate one half cycle during retrace with the yoke connected, and it's hard to tell if disconnecting will put less or more stress on the horizontal output and damper. I think it would be worth the effort to make extender cables.

Electronic M
01-10-2016, 02:46 PM
I have no idea, but I'm not surprised. Running without the yoke doesn't seem wise, as the system is tuned to resonate one half cycle during retrace with the yoke connected, and it's hard to tell if disconnecting will put less or more stress on the horizontal output and damper. I think it would be worth the effort to make extender cables.

I agree. As someone who has run a CTC-15 without the yoke I can say that it will loose more than half it's HV without the yoke connected (and that should approximately go for the CTC-5 too). Like o_t_n, and I said earlier the yoke is part of a tuned circuit (the horizontal stage), so do not expect it to work correctly without the yoke.